Hello, everyone. In this lesson, we are going to be talking about activated carriers and how energy is exchanged between different chemical processes inside of the cell. Okay. So, we all know that cells need energy to survive and do all the different biological reactions that they have to do. Now, how does this actually happen? Well, energy is going to be delivered to the cell and transported around the cell and between chemical reactions via activated carriers. So energetically favorable and unfavorable reactions can be coupled together because that free energy that is released from one reaction can then be used to fuel the second reaction. This is commonly called reaction coupling or simply just coupling, and it is defined as using energy from one reaction to fuel another. Generally, the reaction that provides the energy is going to have a negative delta g. It's gonna be a spontaneous reaction that releases energy. And then all of that energy that was released from the chemical reaction is going to be put into a positive delta g reaction, which is going to require energy to function. Now, how does this energy actually move around? It isn't really just spit out and then used. It's actually gonna need carriers to get that energy from place to place, and these are gonna be called activated carriers. And they are going to be small molecules responsible for energy storage and electron transfer. Remember, electrons have energy, and they can be utilized to provide energy to chemical reactions. So you'll commonly hear activated carriers also be called electron carriers if they actually do carry energy in that form. Now, these are going to contain rich covalent bonds, and these bonds in activated carriers are broken and then energy is released, and then that energy is gonna be used to fuel the next reaction. So, energetic coupling is the foundation for cellular metabolism. It is gonna be the way that we actually move energy around the cell and from different chemical reactions so that all of these different things can happen at the same time and, at the same rate and at a nice continuous pace of life.
A great example of an activated carrier is going to be one particular molecule that I'm sure you have all heard before, and we are all familiar with, and that is gonna be the marvelous ATP. It is going to carry energy. Right? Whenever we talk about ATP, we always say it is the energy molecule of the cell or energy carrying molecule of the cell. And that is because it is one of the activated carriers that we just talked about. It's gonna be the most famous one. You're gonna hear it a ton. You're gonna talk about ATP and its ability to carry energy all the time. So, ATP is going to be Adenosine Triphosphate. It's gonna have 3 Phosphate Groups attached to it. So that's the ATP part here. And then, whenever you break off one of those phosphate groups, it releases energy every time you break off one of those phosphate groups. And when you break off one of those phosphate groups, that's gonna be a favorable reaction, and you release energy. So, whenever you break off that phosphate group, which is right here, whenever you break it off, energy comes out of that breaking of those covalent bonds. Now, that turns Adenosine Triphosphate from having 3 Phosphates to having 2, and now it's gonna be called Adenosine Diphosphate or ADP. So, energy is released from ATP turning into ADP, and then this energy is going to be put towards a different unfavorable reaction. And unfavorable means that it needs energy. So, it requires energy to do whatever it may do. There's gonna be tons of reactions that require energy inside of our cells. So this is just a generic example, but let's say that you have these 2 molecules that the cell wants to turn into these 2 molecules, but that reaction is not spontaneous. It's not just gonna happen on its own. So the cell is going to have to put energy into this reaction, and it's commonly going to utilize ATP and the breaking down of ATP to do this process. So, a great example of this would be if you wanted to transport a particular molecule across the cell membrane against its concentration gradient, that's gonna require energy because the cell the molecule can't simply get across the cell membrane, and it's going to go against its concentration gradient. This is very difficult to do because this is not gonna happen spontaneously. The cell takes ATP and gives it to a transport protein, and then that transport protein utilizes the energy to move that molecule. One reaction releasing energy, ATP turning into ADP. So then that transport protein simply uses the energy from ATP to move that molecule. So that's a great example of our cells using those ATPs. And if you want more information on that, we have a whole bunch of different lessons on cellular transport where we talk about those types of transport that require energy. But let's continue on. So now let's talk more about different types of activated carriers. I already talked about ATP, but then there's also NADH and NADPH. These are going to be the 2 most common activated carriers. So, ATP and NADH are gonna be the most common activated carriers. There's also another one you should know which is gonna be FAD and FADH2. So those are also gonna be different types of activated carriers. We talk about those in things like cellular respiration and photosynthesis. So, like I already said, ATP stands for Adenosine Triphosphate, and it contains 3 high-energy phosphate bonds. ATP is going to be generated via photosynthesis, we know this, and cellular respiration. So all of this, these processes, cellular respiration, which we do in our cells, and photosynthesis, which plants do in their cells, are going to generate these very important ATP energy molecules. And when ATP is broken through hydrolysis, it releases that energy. Remember, when one of those phosphate groups is broken off, energy is gonna be released. That energy can then be used for a different reaction. We also have NAD+ This NAD+ molecule is going to be utilized to store energy and hydrogen atoms and electrons. So, it is going to store high-energy electrons. Remember how I said electrons can be used for energy? NAD+ is going to do that. It is going to gain electrons and it's going to lose electrons. When NAD+ gains an electron or when it is reduced, it's going to turn into NADH. That is the energy carrying molecule. It has the electron inside of it, and it has the energy. So this one, right here, this version has the energy. This one does not. No energy. So whenever NAD+ accepts an electron it then turns into NADH, and it now has energy which it can give to a different type of reaction. So it is reduced. Just remember that whenever NAD+ gains an electron, that's gonna be powering a different reaction, it is gonna be oxidation. So loss of electrons is oxidation, which you can remember with this nice little saying, Leo says GR. LEO, loss of electrons is oxidation. GER, gain of electrons is reduction. Okay? So NAD+ turns into NADH when it has that very energetic electron that it is carrying, and then when it donates that energetic electron to another reaction to power that reaction, it turns back into NAD+ Okay. So, now let's go down, and these are going to be some structural examples of NAD+ So, this one right here is NAD+. Which is going to be a carrier that when it gets its electron becomes an activated energy carrier. Okay? So that's what NAD+ looks like, and this is what ATP looks like. So this is ATP. It has these 3 phosphate groups. 1, 2, 3. And remember, I told you that whenever you cut this one off, energy is released. And this is going to be the process that we utilize to energize most of our chemical processes inside of our cells. And the reason it's called adenosine triphosphate is because it has an adenine base right here, and it has 3 phosphate groups attached to it. I hope that was helpful. Remember, activated carriers are going to carry energy and carry electrons, which are gonna be utilized to power other chemical reactions inside of the cell. Okay, everyone. Let's go on to our next topic.
